The invention relates to an anemometer for quantity measurement of gases or fluids, in particular for determining an air quantity intake of an internal combustion engine through a channel, having a block-shaped substrate of low thermal conductivity arranged in a channel, having on at least one surface of the substrate a temperature-dependent surface resistor, current connecting means to the surface resistor, and a holder for the substrate.
To achieve in particular for internal combustion engines an optimum combustion sequence, accurate information on the respective air quantity intake must be available. The ignition point, the fuel quantity to be injected and similar can be controlled as a function thereof.
Anemometers are available in a wide variety of designs. Conventional anemometers operate on the constant-temperature principle, as set forth in German patent application DE-AS 26 49 040. To determine the air quantity measurement, a bridge circuit is used in which a temperature-dependent resistor is located. This resistor is electrically heated and subjected to the flow of the fluid to be measured. An electrical control circuit ensures that the heated electrical resistor is heated to a constant temperature. Measurement of the flow through the bridge permits conclusions to be drawn as to the air quantity flowing past the resistor. A second temperature-dependent resistor can be connected in a second bridge leg to compensate for the effect of the intake air temperature.
A time variation in the characteristic curves should be avoided partly by the design of the temperature-dependent resistors and their arrangement in relation to the air flow. The selection and the design of the substrate supporting the resistor are intended to ensure that thermal inertias of the substrate are largely ruled out, to ensure rapid recording of the air quantity or of changes thereto.
As regards the current connecting means, it may be noted that these can be designed in the form of wires, for example, or by soldering or by conductive adhesive attachment to a conductive holder.